In 1994 the United States imported 665,000 tons of peat and harvested 574,000 tons of peat locally. Of the locally produced peat, over 60% was used in general soil improvement and in potting soils. In Russia and Europe, millions of tons of peat are used as a fuel and as a raw material for the production of coke. These Russian and European applications of peat exploit its moderate calorific value, carbon content, and generally low ash content compared to coal. Previously, granulated peat has not been used as a fuel because of the added cost associated with converting raw peat into granules and because most fuel uses involve large scale mechanical handling.
Most of the peat used in the U.S. is packaged in bags, bales or supersacks. In order to render the peat suitable for packaging in these forms, it is generally dried after harvesting and then either macerated or hammermilled to improve its handling characteristics. Even after this treatment, peat is difficult to handle, has a tendency to clump, and is not easy to spread in thin layers, for example, on soil. In addition, loose peat, when partially dried, is very dusty. The dustiness becomes worse as the water content of loose peat is reduced. The dust is brown and can be acidic on the skin, making peat handling operations potentially an unpleasant task.
Loose peat has a variety of uses. It is used as a culture medium for earthworms and mushrooms, as an additive to fertilizers, as a seed inoculant, and for many horticultural and turf-raising purposes. Peat is also used as a chemical spill absorbent, especially as an oil absorbent. The very high oil absorbency of peat is widely exploited in the oil industries of the Southern U.S. Peat also absorbs many times its own weight of water, and has useful ion exchange properties. Peat is therefore used to filter water, and is especially useful for removing heavy metals from water.
Peat is generally dried to about 50% water content before harvesting or before packaging. Transportation of such peat carries a cost penalty because of the high water content. On the other hand, if loose peat is dried to less than about 35% water, it is usually very dusty to handle.
In Europe and Russia, peat is used in the chemical and health care industries. Chemicals that can be extracted from peat includes waxes, bitumen, resins, carbohydrates, humic acids, lignin and pectins. With regard to health care, peat is used in peat baths and contains a variety of pharmacologically active ingredients.
Peat is naturally slightly acidic in nature due to the presence of humic acids. As an animal litter, peat has the useful property of absorbing and neutralizing urea, thus controlling the odor of urine. For example, U.S. Pat. No. 5,060,598 claims the use of peat to control odor in cat litter. On the other hand, the acidity of peat is often disadvantageous in horticultural use, and it has to be counteracted by addition of a basic chemical such as lime. It would be desirable if there was an easy way to control the pH of commercially supplied products incorporating peat.
Organic materials are commonly prepared in granular form by one of two methods: high pressure extrusion or pelletization. High pressure extrusion is very widely used to prepare foods such as breakfast cereals and pet foods. The extruders used are called "cooker-extruders" and they induce very high shear into the material towards the exit end of the extruder. This produces a high temperature for a short time. This high temperature sterilizes the food and gelatinizes the starches in the formulation. Extrudates from cooker extruders are consolidated to close to the maximum density due to the high pressures, but lower densities have been achieved by inclusion of a blowing agent which causes the composition to generate gas bubbles as it exits the high pressure extruder. Such techniques are not suitable for making peat granules, because the aggressiveness of these processes tends to destroy the beneficial properties of the peat.
Other organic materials, such as saw dust and waste paper, are made into granules by use of a pellet mill. Pellet mills operate on blends of dry materials with low water content. The materials are forced through the holes in the die by rollers. The pressure generated in pellet mills is extremely high, and very dense granules with low porosity due to low void space are produced by pellet mills. In principle, peat could be pelletized using a pellet mill, but the resulting pellets would be dense and would not possess all the beneficial properties offered by this invention.